Cash, Cash Equivalents, and Investments

Cash, cash equivalents, and investments consisted of the following (in thousands):



	March 31, 2019		December 31, 2018
Cash	$	94,413	$	104,655
Money market instruments	10,883		3,557
Cash and cash equivalents	105,296		108,212
Treasury bills	189,808		198,477
Corporate bonds	137,228		137,871
Asset-backed securities	98,910		78,407
Sovereign bonds	10,900		8,101
Municipal bonds	4,491		4,492
Current investments	441,337		427,348
Corporate bonds	152,645		162,566
Treasury bills	105,298		32,760
Asset-backed securities	41,460		53,631
Sovereign bonds	10,891		6,316
Agency bonds	5,913		5,921
Municipal bonds	847		845
Non-current investments	317,054		262,039
	$	863,687	$	797,599

Treasury bills consist of debt securities issued by the U.S. government; corporate bonds consist of debt securities issued by both domestic and foreign companies; asset-backed securities consist of debt securities collateralized by pools of receivables or loans with credit enhancement; sovereign bonds consist of direct debt issued by foreign governments; municipal bonds consist of debt securities issued by state and local government entities; and agency bonds consist of domestic or foreign obligations of government agencies and government sponsored enterprises that have government backing. All securities are denominated in U.S. Dollars.

The following table summarizes the Company’s available-for-sale investments as of March 31, 2019 (in thousands):



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
Current:
Treasury bills	$	189,599	$	211	$	(2	)	$	189,808
Corporate bonds	137,294		87		(153		)	137,228
Asset-backed securities	98,902		135		(127		)	98,910
Sovereign bonds	10,898		14		(12		)	10,900
Municipal bonds	4,492		—		(1		)	4,491
Non-current:
Corporate bonds	152,668		329		(352		)	152,645
Treasury bills	104,987		332		(21		)	105,298
Asset-backed securities	41,342		130		(12		)	41,460
Sovereign bonds	10,876		15		—			10,891
Agency bonds	5,930		—		(17		)	5,913
Municipal bonds	855		—		(8		)	847
	$	757,843	$	1,253	$	(705	)	$	758,391

The following table summarizes the Company’s gross unrealized losses and fair values for available-for-sale investments in an unrealized loss position as of March 31, 2019 (in thousands):



	Unrealized Loss Position For:
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses
Corporate bonds	$	63,106	$	(253	)	$	74,227	$	(252	)	$	137,333	$	(505	)
Treasury bills	62,560		(23		)	—		—			62,560		(23		)
Asset-backed securities	5,476		(4		)	38,434		(135		)	43,910		(139		)
Sovereign bonds	3,458		—			4,628		(12		)	8,086		(12		)
Agency bonds	5,913		(17		)	—		—			5,913		(17		)
Municipal bonds	1,301		(1		)	847		(8		)	2,148		(9		)
	$	141,814	$	(298	)	$	118,136	$	(407	)	$	259,950	$	(705	)

As of March 31, 2019, the Company did not recognize any other-than-temporary impairment of these investments. In its evaluation, management considered the type of security, the credit rating of the security, the length of time the security has been in a loss position, the size of the loss position, the Company's intent and ability to hold the security to expected recovery of value, and other meaningful information. The Company does not intend to sell, and is unlikely to be required to sell, any of these available-for-sale investments before their effective maturity or market price recovery.

The Company recorded gross realized gains and gross realized losses on the sale of debt securities totaling $64,000 and $24,000, respectively, during the three-month period ended March 31, 2019 and $55,000 and $33,000, respectively, during the three-month period ended April 1, 2018. These gains and losses are included in "Investment income" on the Consolidated Statement of Operations. Prior to the sale of these securities, unrealized gains and losses for these debt securities, net of tax, are recorded in shareholders’ equity as other comprehensive income (loss).

The following table presents the effective maturity dates of the Company’s available-for-sale investments as of March 31, 2019 (in thousands):



	<1 year		1-2 Years		2-3 Years		3-4 Years		4-5 Years		5-7 Years		Total
Treasury bills	$	189,808	$	105,298	$	—	$	—	$	—	$	—	$	295,106
Corporate bonds	137,228		102,129		35,329		12,360		2,827		—		289,873
Asset-backed securities	98,910		19,283		8,119		7,767		3,425		2,866		140,370
Sovereign bonds	10,900		3,499		7,392		—		—		—		21,791
Agency bonds	—		—		—		5,913		—		—		5,913
Municipal bonds	4,491		847		—		—		—		—		5,338
	$	441,337	$	231,056	$	50,840	$	26,040	$	6,252	$	2,866	$	758,391